1. Technical Field of the Invention
The present invention relates to balun networks, and more particularly, relates to balun networks having selectable port impedances.
2. Description of the Related Art
Radio designers typically chooses components and feed lines having standard impedances such as 300 Ohms, 75 Ohms, or 50 Ohms, for example. Such standard impedances match the impedances of existing standard components. These include balanced-unbalanced networks or balun networks. Known balun networks have fixed impedance ratios between the balanced and unbalanced inputs and outputs. For example, most baluns such as split sheath and bazooka baluns have impedance ratios of 1:1. Thus, the input impedance is the same as the output impedance. Other baluns such as a half-wave balun has an impedance ratio of 4:1, wherein the balanced port has an impedance four times the impedance of the unbalanced port.
Radio frequency functions have been implemented in integrated circuit chips. Many integrated circuit chips have balanced connections while other components on a printed circuit board require unbalanced connections. Implementing baluns with fixed impedance ratios for coupling to standard impedances of radio frequency components places an impedance requirement constraint on the design of an integrated circuit.